1. Field of the Invention
The present invention relates to an adaptive dryer method and apparatus for controlling drying of printed pages of a printer based on determined mass-area coverage of ink on the pages. More specifically, the present invention relates to an adaptive dryer which, based on the determined mass-area coverage, varies one or both of feed rate of the pages through the dryer and temperature of the dryer.
2. Description of Related Art
Most printers utilize one of two methods of image fixing, either naturally air drying the image or routing the image to a heating unit for standard drying of the image. A common problem with air drying is an excessive amount of time, upwards of 30 seconds per page, which is needed to provide adequate drying. Drying with a heating unit to aid in fixing of the image requires the heating unit with sufficient power capacity to fix all or most images presented. A heating unit of this type utilizes an excess amount of power and additionally requires increased maintenance costs. The heating requirements for some pages of relatively low area coverage or low mass coverage are minimal and can result in excess energy being applied or excess time being spent drying an image which does not require the preset amount of heating. In addition, heating of pages beyond that necessary may result in overdrying which can distort, warp or otherwise deteriorate the appearance of the page. For example, drying parameters (such as temperature and/or feed rate) are set on a worst case condition for a 50% mass-area coverage image, when most sheets have a 6% mass-area coverage image, thus overdrying the sheets having 6% mass-area coverage image. Further, on some machines, the preset drying settings could cause unnecessary reduction in throughput by utilizing a feed rate of printed pages through the heating unit which is unduly slow due to a preset speed which is determined for a worst case scenario of image fixing requirements. The following are known patents which attempt to address certain problems of these first two types:
U.S. Pat. No. 4,719,489 to Ohkubo et al. discloses a recording apparatus having material dependent fixing control which controls a fixing means of the recording apparatus between first and second conditions dependent upon sensed feed modes. The sensed feed modes relate to papers of different thicknesses. In particular, the apparatus controls fixing temperature, pressure or feed rate therethrough based on detected paper thickness.
U.S. Pat. No. 4,634,262 to Imaizumi et al. discloses a toner image fixing control process and apparatus for an electrostatic copying machine. The apparatus includes a fixing station which normally operates at a fast speed when used for thin sheets, but will slow down when a thick sheet is detected in order to allow for extra time for a toner image on the thick sheet to fuse.
U.S. Pat. No. 3,588,445 to Hopkins discloses a fuser control circuit wherein the amount of power supplied to a fuser is proportional to the speed of paper upon which an image is being fixed. The speed is detected by detecting the width of input signal pulses.
U.S. Pat. No. 4,970,528 to Beaufort et al. discloses a method of uniformly drying ink on paper from an ink jet printer wherein a sheet is transported along a semicircular paper path such that an infrared bulb situated at the axis of symmetry of the semicircular path provides even heating to the entire sheet.
None of these references provides a dryer which closely matches the dryer operating parameters to a particular page's drying requirements based on the area of ink or mass of ink which covers the page.